Don’t believe the naysayers to the handheld devices. None have actually used a modern handheld to be credible with their opinions, which are based on using integrated graphics on a laptop cpu.
I have the Legion Go which has the same core hardware as the ROG Ally, but with a bigger, higher resolution screen. My experience with the device for SL is really good. I run SL at 2560x1600 on high settings with advanced lighting on and shadows off and I get between 33 and 42 frames in Firestorm. The joycons can be used for movement and if you don’t want to bother with a Bluetooth mouse and keyboard the onscreen keyboard can be detached from the taskbar and used as a keyboard for chat. The performance between a Legion Go and a ROG Ally are very close with the same settings in most other games so I would estimate your experience will be similar. Though I think the Legion Go with its bigger higher rez screen will be nicer. I love this device, and being able to take this on the go and still connect with friends in SL is nice.
I also use a desktop with an i9 13900K 128gb and an RTX 4090 and a Legion Pro 5i laptop with an i9 13900HX 32gb and RTX 4060 for SL. Both devices obviously run circles around the little gaming handheld in every way except for portability. My desktop is easily 60lbs and tied to a desk, my laptop is 5 lbs, but the Legion Go is under 2 lbs. I am finding myself going to that when I am in bed or on the couch more than my laptop.